A woman arguing with her boyfriend on the 12th-floor balcony of his Bronx home plummeted to her death yesterday, neighbors said.

Detectives were investigating how Nakia Toro, 26, died – whether she jumped, fell or was pushed from the Parkchester apartment of Her beau around 3 a.m., police sources said.

A downstairs neighbor said she heard a man saying, “No, no, no” followed by a woman’s shriek. “And I heard a thump,” said the neighbor.

Police did not release the boyfriend’s name, but neighbors identified him as Willie Morales and said he works at a medical lab.

The downstairs neighbor, who would not give her name, said she believed Toro threw herself off the balcony. The neighbor said she was once told by Morales’ relatives that Nikki had said to him that “If you’re not going to be with me, I’m going to kill myself.”